The embodiments herein relate generally to electrical communication systems, and more particularly to a radio interference eliminator circuit.
In the field of electronic flow measurement (EFM), signal chirping is a long felt problem that has existed in processing by electronic flow computers for over twenty years. Chirping is a parasitic signal which causes interference in data measurements. Chirping arises when a flow computer's communications control line is powered high. FIG. 1 shows a conventional connection between an EFM computer and data communications device (for example, a radio, modem, etc.). The control voltage powers up the data communications device connected to the EFM computer's receive data input (Rxd) line and transmitter data output line (Txd) to receive and transmit data to the polling EFM computer. The communications control line (“OPERATE”) powers up the communications device, for a set amount of time that is pre-programmed into the EFM computer. If the EFM computer detects a device's identification (ID) or address, the communications control line remains on to allow communication between the EFM computer and the poling computer. The control typically also powers down after the pre-programmed time elapses and the device ID or address is not detected.
Referring now to FIG. 2, a screenshot of a logic analyzer is shown displaying chirping that arises in a conventional EFM measurement circuit. As the control line (labeled on screen as channel “0 OPER”) goes high, the communications device is powered up (represented by the signal on channel “1 DCD”)(also known as the data carrier detect). The communications device now begins to receive data as represented by the channel labeled “2 RUS” and passes data to the EFM Rxd Input (channel “4 RX_BD). As can be seen by FIG. 2, when the control line (Channel “0 OPER”) goes low, the signals from channels “1 DCD”, “2 RUS”, and “4 EFM RX_BD” remain high and there is a lag as the length of the Rxd input signal 20 remains high along with the duration of the communications device R×d line before these signals return to low coinciding with the operate line. During this lag between the EFM Rxd input returning to the low state with the operation line, the EFM Rxd input continues to receive data. However, the Rxd input changes to a high impedance state as the operate line goes to low. The data received by the Rxd input line continues to bounce back and forth between its source, the communications device, and the EFM computer because of the high impedance. Any data in phase with the returning, bouncing data, (the chirp) adds and causes a voltage spike which migrates to the Txd and RTS lines in the EFM computer. This causes the communications device to key up and transmit resulting in interference to the EFM system which lowers system efficiency.
As can be seen, there is a long felt need for a solution to eliminate chirp from this application.